This invention is for a fireplace fuel cartridge, primarily for use in ventless fireplaces although usable in vented fireplaces as well, where the fuel cartridge self regulates the shape, height, width, depth and burn time of the flames produced when the fuel in the cartridge, such as alcohol gel, is ignited, thereby producing a desirable, generally rectangular flame pattern that makes efficient use of fuel, and where the cartridge accomplishes this without a need for additional components such as rectangular holding boxes or damper lids.